1. Field of the Invention
This invention relates to an ink jet head or a liquid jet head, a substrate for ink jet head to be used for forming said head, and an ink jet device having the above-mentioned head.
2. Related Background Art
A typical example of the structure of a liquid jet recording head utilizing heat energy for discharging liquid is shown in FIGS. 1A and 1B. FIG. 1A is a partial front view as seen from the discharge opening side of a liquid jet recording head, and FIG. 1B a partial sectional view when cut along the portion shown by the chain line XY in FIG. 1A.
The recording head 100 has structure having discharging openings or orifices 104 and liquid channels 105 formed thereon by bonding a grooved plate 103 having a predetermined number of grooves of predetermined width and depth provided at a predetermined line density of the surface of a heat-generating substrate 102a including a plate-shaped support 102 having the heat-generating portions 101 of electricity-heat converters provided thereon so as to cover over the surface.
The recording head shown in the Figures has a plurality of discharge openings 104, but a recording head having a single discharge opening has been also known.
The liquid channels 105 are communicated at their terminal ends to the discharge openings 104 for discharging liquid, and have heat-acting portions 106 which are sites or areas where heat energy generated by the heat-generating portions 101 of the electricity-heat convertors act on the liquid. The heat-acting portions 106 are positioned at the upper parts of the heat-generating portions 101 of the electricity-heat convertors, and have the heat-acting surfaces 108 as the surfaces in contact with the liquid as their bottom surfaces.
On the support 102 are provided a lower layer 109, a heat-generating resistance layer 110 provided on said lower layer 109 and a first protective layer 111 comprising, for example, an inorganic insulating material provided on said heat-generating resistance layer 110, etc. The heat-generating resistance layer 110 is provided on its surface side with electrodes 113, 114 for passing current to said layer 110 for generating heat. The electrode 113 is an electrode common to the respective heat-generating portions, while the electrode 114 is a selective electrode for generating heat by selecting the respective heat-generating portions and is provided in a pattern shape along the liquid channel.
In the liquid jet recording head having a constitution as described above, current is passed in pulse shape to the heat-generating portions 101 existing between the electrodes 113, 114 of the heat-generating resistance layer 110 through these electrodes, and liquid is discharged by heating liquid with the heat-acting surface 108. For transmitting efficiently the heat generated at the heat-generating portion 101 during current passage, the lower layer 109 becomes a barrier against transfer to the support 102 during heating, whereby heat is transmitted primarily from the heat-acting surface to liquid. For this reason, as the material forming the lower layer 109, a material with relatively smaller thermal conductivity, for example, an inorganic oxide such as SiO.sub.2, a transition metal oxide such as titanium oxide, niobium oxide, etc. is selected, and diffusion of heat toward the support 102 side is suppressed by the lower layer 109. For example, U.S. Pat. No. 4,458,256 is directed to an ink jet recording apparatus having actuating portions, lead electrodes wired in a particular manner for conducting current, and a recording head including a substrate, an insulating layer, and a conductive layer.
However, in the prior art example as mentioned above, heat may be sometimes accumulated in the lower layer 109 when the recording head is continuously driven for a long time, whereby temperature elevation of the whole recording head 100 may be brought about. Moreover, when such heat accumulation in the lower layer 109 becomes marked, the following phenomenon are liable to be induced:
(1) unstabilization of forming at the heat-acting portion 106 by excessive heat energy transmitted to the liquid during current passage to the heat-generating portion 101 due to temperature elevation of the lower layer 109; PA1 (2) discharge unstabilization due to increased amount of dissolved oxygen precipitated into the liquid channel on account of temperature elevation of the liquid near the heat-acting portion 106, and PA1 (3) increase of the droplets discharged accompanied with temperature elevation. PA1 characterized in that ink channels communicated to discharge openings for discharging ink are formed corresponding to the heat generating portions of said heat energy generating member on said heat generating substrate; and PA1 the thermal conductivity of said intermediate layer is higher than that of said support and higher than that of said lower layer. PA1 characterized in that ink channels communicated to discharge openings for discharging ink are formed corresponding to the heat generating portions of said heat energy generating member on said heat generating substrate; and PA1 the thermal conductivity of said intermediate layer is higher than that of said lower layer. PA1 characterized in that ink channels communicated to discharge openings for discharging ink are formed corresponding to the heat generating portions of said heat energy generating member on said heat generating substrate and the thermal conductivity of said intermediate layer is higher than that of said support and higher than that of said lower layer. PA1 characterized in that ink channels communicated to discharge openings for discharging ink are formed corresponding to the heat generating portions of said heat energy generating member on said heat generating substrate; and PA1 the thermal conductivity of said intermediate layer is higher than that of said lower layer.
When these phenomena (1), (2) and (3) occur, no stable droplet discharging state at the recording head can be obtained, whereby there may be sometimes caused the problem to occur that no stable recording operation with good recording images can be done, particularly in prolonged continuous recording operation.
The background arts concerned as mentioned above are described by referring to other drawings.
The liquid jet recording head utilizing heat energy for discharging liquid for recording such as ink, etc. has a constitution, as shown in FIGS. 2A and 2B, having liquid channels 6 communicated to the orifices 7 through which liquid is discharged provided at the positions corresponding to the heat-generating portions 2a of the heat-generating substrates 8 constituted by arrangement of the heat-generating resistors 2 possessed by the heat energy generating members for generating heat energy which acts on liquid, said liquid channels having liquid chambers 10 for feeding liquid.
The heat-generating substrate 8, as shown in FIGS. 3A and 3B, can be obtained by laminating at least the heat-generating resistance layer 2 and the electrode layer 3 on the substrate 1, subjecting these to patterning into a predetermined shape at predetermined intervals, and forming heat-generating portions 2a connected electrically to a pair of electrodes (3a, 3b). On the electrodes (3a, 3b) possessed by the heat-generating substrate 8 and/or the heat-generating portion 2a, various upper layers such as protective layer 4, etc. may be provided, if necessary. For example, European Patent Application No. 0,289,139 is directed to a substrate for an ink jet recording head having a support member, an electro-thermal converter provided on the support member having a heat generating resistive layer and a pair of electrodes connected to the heat generating resistive layer, and a glaze layer provided between the support member and the electro-thermal converter except at a heat generating portion defined between the pair of electrodes.
As the substrate 1 to be utilized for formation of a heat-generating substrate 8 to be used for the liquid jet recording head of such constitution, plate materials comprising silicon, glass and ceramics, etc. have been employed in the prior art.
A silicon substrate has relatively sufficient performances for use as the substrate for liquid jet recording head, but high degree of technique is required for formation of a substrate with a large size corresponding to enlargement of recording head, and yet the cost is also high.
Further, in a recording head having a glass substrate assembled therein, due to inferior thermal conductivity of glass substrate, when the driving frequency of the pulses imparted to the heat-generating resistors is made higher, excessive heat accumulation may sometimes occur at the substrate portion, whereby the liquid existing within the recording head is heated to include bubbles, and defects such as defective discharging of liquid, etc. are liable to occur.
On the other hand, as ceramics substrate, alumina substrate has been utilized from the points that it can manufacture a substrate with relatively larger size and that thermal conductivity is better as compared with glass. However, because of the manufacturing technique which calcines starting material powder, surface defects such as pinholes or projections with sizes of several .mu.m to several 10 .mu.m are liable to be generated, and its surface roughness is about Rs 0.15 in most cases. As influenced by these, the recording head having an alumina substrate assembled therein has short durability life in many cases. Moreover, improvement of the surface characteristic of an alumina substrate having surface defects by mechanical treatment is extremely difficult, because alumina itself is a material of high hardness.
As the substrate compensating for the defects of alumina substrate, there has been known the so called alumina glaze substrate improved in surface roughness by coating the surface alumina with molten glass. However, the glaze layer comprising glass possessed by the alumina glaze substrate is limited in making its layer thickness thinner (about 40-50 .mu.m or less) in its preparation method, and therefore there may be sometimes caused the problem of excessive heat accumulation in the substrate to occur similarly as in the case of glass substrate.
Also, the substrate for recording head is required to have good balance of heat accumulatability and heat dissipatability, and there is also a constitution having additionally a heat accumulation layer provided on the substrate surface for taking the balance of these. For example, in the case of such substrate equipped with such heat accumulation layer by use of ceramics such as alumina, etc., a film of low thermal conductivity such as SiO.sub.2 layer, etc. has been formed on the predetermined surface of a ceramics plate material by use of vacuum film forming technique such as sputtering.
However, by film formation according to vacuum film formation technique, there have been involved such problems that the film forming speed is slow, and yet dust, etc. may be sometimes also entrained during film formation, and also no heat accumulation of sufficient quality can be obtained in many cases.